Industrial machinery often requires lubricating compositions, for example gears, bearings, couplings, and pumps. Additives in the lubricating compositions are often used to help to improve the operational qualities of the lubricants depending upon the conditions of operation.
U.S. Pat. No. 5,236,610 relates to an antioxidant additive for an engine or propulsion system lubricant subjected to high temperatures which includes a high molecular weight substituted phenolic carboxylic acid tetraester of pentaerythritol. A lubricant blend which is capable of solubilizing the antioxidant additive includes a polyolester, a phosphate ester and at least one of a polyalphaolefin and alkylated naphthalene. Specifically claimed compositions are a liquid lubricant comprising a mixture of 25-65 weight percent of a polyolester, 5-15 weight percent of a phosphate ester, 25-65 weight percent of at least one synthetic hydrocarbon selected from the group consisting of a polyalphaolefin and an alkylated naphthalene, and an effective antioxidant amount of at least one compound selected from the group consisting of phenyl naphthylamine, diphenylamine, a methylene bis(dialkyl-dithiocarbamate), a methylene bis(diaryl-dithiocarbamate), a 2,6-dialkyl-p-cresol, a bisphenol of a 2,6-dialkyl-p-cresol, and a tri-substituted phosphite. All of the lubricants require both polyolester and phosphate ester.
U.S. Pat. No. 5,275,749 relates to the lubricating compositions containing an N-acyl-N-alkoxyalkyl aspartate ester, optionally in further combination with an anti-wear agent. The compositions are said to exhibit corrosion inhibition and anti-wear properties. Dialkyl carbamate and arylamine are mentioned as additives. The base oils can include synthetic hydrocarbon base oils, but alkylated naphthalene is not mentioned.
U.S. Pat. No. 6,326,336 relates to a turbine lubricant consisting of (A) alkylated diphenylamine and/or phenylnaphthylamines, and (B) sulfurized olefins and/or sulfurized fatty acids and/or ashless dithiocarbamates and/or tetraalkylthiuram disulfides, with the balance containing (C) base oils characterized by very low sulfur contents (<0.03 wt %) and a high level of saturates (>90 volume %), and optionally (D) neutral rust inhibitors. A particularly claimed composition is a turbine lubricating oil comprising (A) an amine antioxidant comprising a mixture of alkylated diphenylamines and phenyl-naphthylamines; (B) a sulfur-containing additive selected from the group consisting of sulfurized olefins, ashless dithiocarbamates, tetraalkylthiuram disulfides and mixtures thereof; and (C) a base mineral oil having a sulfur content of less than 0.03 wt % and greater than 90 volume % saturates. The base oil stocks are said to not include Group V base stocks.
GB2363128 relates to industrial oil compositions which require trimeric organo molybdenum compounds as antioxidants and uses a combination of dithiocarbamate and arylamine in comparative examples. The base stock is selected form Group I, II, III and IV.
U.S. Pat. No. 6,599,865 relates to a lubricating composition comprising a major amount of lubricating oil, and a minor amount of an oil soluble alkylated diarylamine, an oil soluble alkylated phenothiazine, and an oil soluble sulfurized compound, said sulfurized compound selected from the group consisting of sulfurized olefins and sulfurized fatty oils. This patent discloses that it has unexpectedly been found that the combination of (1) an alkylated diphenylamine, (2) a sulfurized olefin/fatty oil and/or an ashless dialkyl dithiocarbamate, and (3) an alkylated phenothiazine, is highly effective at controlling crankcase lubricant oxidation and deposit formation. There is no mention of using alkylated naphthalene as the base oil, and the patent requires the three component additive system.
U.S. Pat. No. 6,806,241 relates to antioxidant compositions comprising (1) an organo molybdenum compound, (2) an alkylated diphenylamine, and (3) a sulfur compound selected from (a) thiadiazole, (b) a dithiocarbamate and (c) a metal dithiocarbamate. There is no mention of alkylated naphthalene as the base oil.
Pub. U.S. 20070129268 relates to a lubricating oil composition containing one or more hydrocarbyl-substituted aromatic lubricant base oils in combination with (a) one or more phenyl-naphthylamines, and (b) one or more diphenyl amines, where said lubricating oil composition comprises one or more additional lubricant base oils comprising polyalphaolefin and/or Fischer-Tropsch derived base oils. It is said that the disclosure relates to the use of the lubricating oil composition for lubricating a rotary air compressor. The only mention of dithiocarbamates is as the molybdenum complex, said to be suitable as an anti-wear additive.
EP2159275 relates to a lubricating composition comprising base oil selected from the group consisting of Fischer-Tropsch derived base oil and a poly-alpha olefin (PAO) base oil or a combination thereof; a detergent; and an amine compound. Dithiocarbamates and aryl amines are exemplified and alkylated naphthalene is mentioned as a possible component of the base oil.
Pub. U.S. 20100197537 relates to a lubricant composition said to have improved antioxidant capability which includes an additive composition containing a metal free sulfur-containing compound, an aromatic amine, and a hindered amine Particularly effective metal-free sulfur-containing compounds are said to include ashless dithiocarbamates, such as ethylenebis (dibutyldithiocarbamate), and sulfurized fatty acids.
The operating temperature and efficiency of any lubricating composition is especially important to the designers, builders, and user of certain industrial machinery. Next generation synthetic industrial lubricants will have higher performance demands such as step-out thermo-oxidation performance. Formulations able to demonstrate a higher level of performance will have longer oil life and increased drain intervals. Other attributes for these fluids include higher temperature capability and reduced environmental footprint.
Oxidative stability is key in achieving long oil life. Controlling oil viscosity increase through identifying robust performing base stock and additive combinations can minimize deposit (varnish/sludge) formation, and maintain good heat transfer and lubricating properties, including efficiency. The reduced oxidation, and thus increased performance of a lubricant, is especially desirable in high temperature applications and environments. Oxidation testing is an important part of assessing the potential stability of a lubricant for use in most lubricating applications including air compressors and gear oils. The high volumes of air and high temperatures experienced by a lubricant in an air compressor can have a large effect on the lubricant's oxidative stability. Assessing the stability of a lubricant in oxidation tests are methods by which a formulator can determine the potential stability of an air compressor lubricant in service. Oxidation tests have been developed to determine the length of time it takes for a lubricant to degrade from oxidation or break to a catastrophic increase in viscosity. These methods are used to evaluate mineral and synthetic lubricants, with or without additives. The evaluation is based on the resistance of the lubricant to oxidation by air under specified conditions as measured by the changes in viscosity.
Total acid number (TAN) increase in a lubricant is a sensitive way to detect oxidation of the base oils and additives. TAN measures the by-products of oxidation. Upward trending TAN can determine the rate of depletion of additives, as well as indicate when oxidation rate significantly increases, rendering the fluid potentially harmful to the equipment. Common problems for the equipment caused by an oxidized lubricant are corrosion and deposit formation. Increasing the time to reach TAN limits is a valuable gauge of the quality of the performance of a lubricant. Oil life is determined when the TAN reaches a prescribed limit. The limit is nominally set in two ways: approximately 2.0 mg KOH/g above the baseline TAN; or the time in which the lubricant shows a significant slope change (vertical) from the previously determined value.
Kinematic Viscosity (KV) increase is another measure that is commonly used to determine oil failure due to oxidation. Tests conducted in high temperature (170° C.) environments with a catalyst, are a means to measure whether any particular oil has a longer oil life when compared to references.
For measuring KV increase, the sample is placed in an oxidation cell together with various organometallic catalysts that are dissolved in solution and then placed into the test cell. The cell and its contents are placed in a heating block maintained at a specified temperature, and a measured volume of dried air is bubbled through the test cell held at a pressure ranging from 0-100 psig for the duration of the test, with an air flow rate up to 250 cc/min. A constant temperature block, equipped with an electric heater and thermostatic control capable of maintaining the temperature within +/−1° F. (0.5° C.) in the range of 200° F. (93° C.) to 450° F. (232° C.) is used to maintain the specified temperature.
Periodically the test cell is sampled for viscosity until the oil has oxidized. The oil condition is examined by measuring its KV at a specified temperature. Comparisons can then be made to the original KV of the oil. The time at which it takes the oil to reach a catastrophic increase in viscosity (200%) is used to determine the endpoint of the test.
Thus, it is an object of the present disclosure to provide a lubricant composition which has reduced oxidation over conventional lubricants.
It is also an object of the present disclosure to provide a lubricant composition which has longer time-to-TAN or viscosity increase characteristics as compared to the lubricants presently in use.
It is a further object of the present disclosure to provide a lubricant composition having better high temperature performance as compared to lubricants presently in use.
It is a still further object of the present disclosure to provide an additive composition for use in lubricants which provides improvement to the above-mentioned characteristics of lubricant compositions, including extending oxidation performance, and reducing corrosion and deposit formation.
These and other objects are accomplished by the present disclosure which will now be described below.